1. Field
The present disclosure relates to a system and a method for treating a nerve symptom, and more particularly to an implantable electrical stimulation system and methods for implanting said system.
2. Description of the Related Art
Pulsed radiofrequency, often called radiofrequency lesioning in clinical practice, has been used for over 30 years to treat various pain complications such as cervicogenic headaches, occipital neuralgia, whiplash injury, cervical radicular pain, intercostal neuralgia, lumbar radicular pain, lower back pain, zygapophyseal joints dysfunction, discogenic pain, pain associated with the sacroiliac joint, etc. However, there is little evidence of efficacy after long-term observation of such radiofrequency lesioning treatment in clinical report literatures. This is mainly due to the radiofrequency lesioning treatment principle. According to this principle, the RF cannula is placed near the related nerve tissues of the affected area. The whole RF cannula is coated with insulating material, with only 0.5 to 1 cm of the electrode tip being exposed. Continuous high-frequency electrical stimulation produces high temperatures to burn the nerve tissues, so that the analgesic effect is achieved after the treatment.
When the human body's repair function is activated, the burned nerve tissues will repair themselves. The nerve tissues will not grow back to the original shape, however, but instead will grow randomly on the dead nerve tissues and form a neuroma, which is easy to be pressed and damaged, resulting in the recurrence of pain or even more serious pain.
The output waveform of radiofrequency lesioning is called continuous radiofrequency (CRF). The radiofrequency lesioning temperature can be controlled through the output voltage. The application discloses improvements in methods of continuous radiofrequency (CRF). Previously, a high temperature of up to 80 degrees Celsius was necessary for radiofrequency lesioning to destroy the nervous tissues. Eventually, an experiment using egg whites was used to study the three-dimensional effect of heat lesioning of CRF. An electrode was placed into the egg white for stimulation, and the range of egg white protein deterioration due to the effect of heat from the CRF was observed. Through this research, low-temperature and continuous radiofrequency was developed for effective CRF heat lesioning.
In 1998, Sluijter et al. developed a kind of pulsed radiofrequency (PRF). The analgesic effect can last for up to six months after one stimulation session. The stimulation session uses 500,000 Hz, 45 volt high-voltage RF current with 2 stimulations per second and 20 microseconds per stimulation, which is meant to avoid temperature increases in the stimulation process, so that a cycle includes 20 microseconds of stimulation phase and 480 microseconds of silent phase.
Such PRF can avoid heat lesion of the nerve tissues, and this electrical stimulation treatment has been gradually applied to the dorsal root ganglion (DRG). In animal experiments involving 80 degrees Celsius radiofrequency lesioning for CRF and 42 degrees Celsius for PRF tests on the DRG and sciatic nerve of rats, the rats were killed at different time points for tissue sections. The results showed that the DRG and sciatic nerve of the rats all receiving CRF got irreversible damages, and the nerve tissues showed signs of the phenomenon called Wallerian Degeneration. Only a little bit of edema occurred in the DRG and sciatic nerve of the rats receiving PRF, and the rats returned to normal within a week.
PRF technology has gradually replaced radiofrequency lesioning technology since around 2000, and the clinical reports also show that PRF is safe, reliable, and can replace radiofrequency lesioning technology to treat painful diseases. However, a new treatment method usually takes a very long time to develop in clinical practice, and Evidence Based Medicine needs at least ten years to accumulate sufficient clinical evidences. PRF is still a very new technology; almost just a decade so far. Currently, many people are involved in the research of this technology, and there are more and more related technical documents and clinical evidences, but there is no evidence to prove or distinguish the advantages between PRF and CRF technologies. In addition, the current literature is unclear about the analgesic mechanism of PRF. Sluijter et al. have analyzed the physical properties of PRF: thermal effects are below 42 degrees Celsius, and the magnetic field is approximately equal to the Earth's magnetic field. It is probably that the dense electric field effects affect the nerves mainly responsible for the transmission of pain: C and Aδ nociceptive fibers.
Therefore, there is a need for an improved implantable electrical stimulation system.